Electronic digital signal processing (“DSP”) has become a key technology in practical realization of 100 Gb/s (and higher data rate) dual polarization (“DP”) coherent transmission systems. Thanks to it, the impact of polarization mode dispersion (“PMD”), chromatic dispersion (“CD”) and to some extent nonlinear (“NL”) effects has become a non-fundamental issue. Instead, polarization dependent loss (“PDL”) emerges as the limiting factor, for which DSP can only compensate partially.
To date, the mechanism of the impact of PDL on DP signals is well understood. A single PDL element can cause power (and optical signal to noise ratio (“OSNR”)) inequality between polarization tributaries and loss of orthogonality between initially orthogonal polarization states, depending on the angle between signal and PDL polarization axes. Since these two impairments occur simultaneously during transmission over multiple randomly oriented PDL elements, the statistics of such events was investigated recently.
However, one important aspect such as interplay between NL and PDL effects and its impact on system design has received little attention. For instance, interplay can occur when PDL-impaired signal propagates in optical fiber with Kerr nonlinearities, resulting in additional system penalties. The mechanism of the interplay between NL and PDL effects was investigated in great detail recently. In that work it was necessary to keep PDL elements and signals state of polarization (“SOP”) aligned with respect to each other. Since a signal's SOP changes rapidly during transmission in an optical fiber, the next step should be to conduct a more comprehensive statistical analysis of the interplay between NL and PDL effects.
However, a comprehensive statistical analysis of the interplay of NL and PDL effects has not been investigated yet, even though it is very important for accurate estimation of the risk factors in system design.